[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/) › Anastrozole

[Pharmacology](https://durgical.com/en/pharmacology/) · [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)

# Anastrozole

A breast cancer tablet for postmenopausal women that blocks the enzyme making oestrogen. It can thin the bones and cause joint pain.

Updated 2026-11-01

- Class: [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)
- Enzyme: Aromatase (CYP19A1)
- ATC code: L02BG03
- WHO Model List of Essential Medicines

✂**Aromatase (CYP19A1)**Anastrozole

ⓘ No structure with anastrozole is available. The figure shows exemestane, another aromatase inhibitor, bound in the same active site of human placental aromatase, above the heme.

**Target in 3D:** Aromatase (CYP19A1). PDB structure 3S7S (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3S7S) · Drag to rotate · pinch to zoom

## Mechanism of action

Anastrozole is a non-steroidal triazole that binds reversibly to aromatase, the cytochrome P450 that converts androgens into oestrogens. In postmenopausal women, where peripheral aromatase supplies most oestrogen, it lowers estradiol strongly. Hormone receptor-positive breast cancer cells lose the oestrogen signal that drives their growth.

- Binds reversibly to the heme pocket of aromatase
- Androgens are no longer converted into estrone and estradiol
- Oestrogen levels fall sharply after menopause
- Oestrogen-dependent breast cancer cells stop growing

## Pharmacokinetics

**Absorption**
Well absorbed by mouth

**Metabolism**
Mostly in the liver, which accounts for most of its elimination

**Elimination**
A small fraction leaves unchanged through the kidneys

**Half-life**
About 50 hours, so it is given once a day

## Indications

- Adjuvant treatment of hormone receptor-positive early breast cancer in postmenopausal women [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- First-line treatment of hormone receptor-positive or unknown advanced breast cancer in postmenopausal women [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- Advanced breast cancer that progressed on tamoxifen [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)

## Adverse effects

### Common

- Hot flashes
- Joint pain and stiffness
- Weakness and fatigue
- Rise in total cholesterol
- Low mood

### Serious (rare, important)

- Loss of bone mineral density and fractures
- Ischaemic cardiovascular events in women with pre-existing ischaemic heart disease
- Severe allergic reactions (anaphylaxis, angioedema)

## Contraindications

- Hypersensitivity to anastrozole or any excipient

## Key interactions

**Tamoxifen**
Not used together: the combination adds no benefit over tamoxifen alone.

**Oestrogen-containing products**
May weaken the effect of anastrozole.

## What is monitored

- Bone mineral density
- Cholesterol
- Joint symptoms and quality of life

## Administration and safety

- Oral tablet, taken at the same time each day with or without food.
- Hazardous drug: people who are pregnant should avoid handling crushed or broken tablets.
- Look-alike names: anastrozole and letrozole are both aromatase inhibitors, but their tablets are not interchangeable.

## Nursing care

- Ask about menopausal status: the drug is meant for postmenopausal women.
- Teach about joint pain and hot flashes, which are common and often manageable.
- Encourage calcium, vitamin D, weight-bearing exercise and bone density checks as planned.
- Ask about chest pain in women with known heart disease.
- Ask about oestrogen products, including some herbal or vaginal products, and report them.

## Pregnancy and breastfeeding

Can cause fetal harm; women who could become pregnant use effective contraception during treatment.

## Memory aid

AnASTrozole shuts the ASTral factory: the fat stops turning androgens into oestrogen, the tumour starves, and the bones pay the bill.

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzyme does anastrozole inhibit?

Aromatase (CYP19A1), which converts androstenedione and testosterone into estrone and estradiol.

## A woman on anastrozole asks why she needs a bone density scan. What is the reason?

Lowering oestrogen speeds bone loss; anastrozole decreases bone mineral density and raises fracture risk, so bone density is checked.

## Why is anastrozole not given together with tamoxifen?

In the trial that compared them, the combination gave no extra benefit over tamoxifen alone.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/anastrozole/)

## Related drugs

- [Letrozole](https://durgical.com/en/pharmacology/letrozole/)
- [Exemestane](https://durgical.com/en/pharmacology/exemestane/)
- [Tamoxifen](https://durgical.com/en/pharmacology/tamoxifen/)

## Related conditions

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)

[← Back to the class: Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Anastrozole: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a696018.html) (MedlinePlus (U.S. National Library of Medicine), 2018); [DailyMed - ANASTROZOLE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=19251d0b-279a-49f5-99b2-0e74d7cca479) (DailyMed (U.S. National Library of Medicine), 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L02BG03) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [Crystal structure of human placental aromatase complexed with breast cancer drug exemestane](https://www.rcsb.org/structure/3S7S) (RCSB Protein Data Bank, 2012).

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Representative model, for educational purposes only.

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